1. Field of the Invention
The present invention relates to a method and apparatus for cutting off fuel of a fuel cell vehicle, and in particular relates to technology for cutoff processing of fuel supply following stopping of power supply to accessories such as an air compressor used for driving a fuel cell.
2. Description of the Related Art
Conventionally, as a power supply cutoff device mounted on a vehicle, there is known a power supply cutoff device for an electric vehicle as disclosed for example in Japanese Unexamined Patent Application, First Publication No. Hei 6-46502. In this electric vehicle, the vehicle is driven by electric power supplied from a drive power supply, and in the case where the power supply cutoff device detects a vehicle abnormality such as a vehicle collision or near miss with an obstacle, or a short circuit in the drive power supply, or in the case where there is a high likelihood of an abnormality occurring, this cuts off the output from the drive power supply.
In such a power supply cutoff device, there is provided an acceleration sensor for detecting acceleration (or deceleration) of the vehicle, and collision judgment is performed by detecting an acceleration change of the vehicle by means of an acceleration signal output from this acceleration sensor. In the case where it is judged that a collision has occurred, then a contact point is opened for example at an output terminal end of a power storage unit such as a battery, or at an appropriate position inside the battery.
As a result, the situation where an output terminal of the battery, and the frame etc. of the vehicle come in contact and short circuit due for example to a shock or vibration at the time of a collision, or where wires are cut into due for example to deformation of the vehicle at the time of a collision giving an open circuit, is prevented.
However, in this power supply cutoff device for an electric vehicle according to the aforementioned related art example, when the power supply from the drive power supply is cutoff at the time of a vehicle collision or the like, the power supply to the accessories such as an air compressor used for driving a fuel cell is stopped.
Here, when operation of the air compressor is stopped, an appropriate time delay occurs from after the power supply is stopped until the motor for driving the air compressor actually stops. Consequently, a situation results where air continues to be supplied, as reaction gas with respect to an air electrode of the fuel cell, and as a pressure signal with respect to a pressure control valve for fuel supply. Accompanying this, fuel (hydrogen gas) of an amount corresponding to the air supply amount is supplied to the fuel electrode of the fuel cell.
At this time, if the output side of the fuel cell is cutoff with respect to the electrical load of for example the accessories for driving the fuel cell such as the motor for driving the air compressor, or the propulsion motor and the like, the output voltage from the fuel cell rises to a no load condition (for example OCV: open circuit voltage).
That is to say, since the output from the fuel cell is not extracted, the situation results where the open circuit voltage continues to be output. Furthermore, since the air compressor is stopped, the air pressure drops, and when this eventually becomes atmospheric pressure, the consumption of fuel (hydrogen gas) in the fuel cell drops so that the high pressure condition of the hydrogen gas continues.
As a result, an unbalance occurs where a tolerance in the inter-electrode pressure (that is to say between the air electrode and the fuel electrode) of the solid polymer membrane type fuel cell is exceeded, so that there is a possibility of deformation or damage of the solid polymer electrolyte membrane inside the fuel cell.
The present invention takes into consideration the above situation, with the object of providing a method and apparatus for cutting off fuel of a fuel cell vehicle which, in the case where power supply to accessories for driving the fuel cell is cutoff, can prevent the occurrence of degradation or damage to the fuel cell, and which can prevent the occurrence of an unbalance where inter-electrode pressure due to air and fuel being supplied to the fuel cell exceeds a tolerance.
In order to resolve the above problems and achieve the related object, the present invention involves: detecting (for example with acceleration sensors 23R, 24L, 25F, 26c and in step S03 in a later mentioned embodiment (the same applies hereunder)) an acceleration (for example an acceleration G) acting on a fuel cell vehicle having a fuel cell power generation system (for example a fuel cell 11 and a power storage unit 12) as a power supply, cutting off fuel supply (for example with a hydrogen cutoff valve 20 and in steps S04-S06) from a fuel supply device (for example a fuel supply section 16) to a fuel cell (for example a fuel cell 11) of the fuel cell power generation system based on the detected acceleration, and cutting off (for example by a storage unit contact breaker 19a, a propulsion motor contact breaker 19c, and in step S07-S08) at least one of a power supply line of a propulsion system (for example a propulsion motor 13, an inverter 14) of the fuel cell vehicle, and a power supply line of an accessory drive system (for example an air compressor 17, a compressor drive inverter 18) of the fuel cell power generation system, alter the supply of fuel has been cutoff (for example. a cutoff control section 21), based on the detected acceleration.
As a result, at the time for example where a vehicle collision occurs, at first the power supply from the fuel cell to the load such as the propulsion motor is cut off, and also the fuel supply, that is the supply of hydrogen gas, to the fuel electrode of the fuel cell is stopped.
At this time, the pressure of the hydrogen gas in the fuel electrode of the fuel cell becomes a high pressure condition. However since air is supplied to the air electrode of the fuel cell from the fuel cell drive device such as the air compressor, the inter-electrode pressure of the solid polymer electrolyte membrane inside the fuel cell is maintained within the predetermined tolerance, and the hydrogen gas in the fuel electrode is consumed so that the pressure of the fuel electrode side is gradually reduced.
Then, by stopping at an appropriate timing, power supply from the power storage unit (for example the power storage unit 12) which constitutes the fuel cell power generation system to the fuel cell drive device, the pressure of the air on the air terminal side can be reduced so as to follow the pressure drop at the fuel electrode side, so that the pressure at both electrodes can be gradually reduced without a significant change in the inter-electrode pressure.
As a result, this can prevent for example the occurrence of deformation or damage of the solid polymer electrolyte membrane, and contribute to the prolongation of the life span of the fuel cell.
In the present invention, the construction may be such that the power supply cutoff section is operated to cutoff power supply, after delaying for a predetermined time from after operating the fuel supply cutoff section to cutoff the supply of fuel (for example the processing of a cutoff delay processing section 36c).
As a result, a delay time from operating of the fuel supply cutoff section until operating the power supply cutoff section, is set beforehand based on for example the size of the piping or manifold for the hydrogen gas, and also the power consumption in the fuel cell drive device such as the air compressor, so that the solid polymer electrolyte membrane can be even more reliably protected.
Furthermore, according to the present invention, in cutting off the supply of fuel, the construction may involve judging if the acceleration has exceeded a predetermined first threshold acceleration (for example a first threshold acceleration G1) (for example step S04), and in the case where the acceleration has exceeded the first threshold acceleration, cutting off fuel supply from the fuel supply device to the fuel cell (for example step S05, S06). Moreover in cutting off the power supply, the construction may involve judging if the acceleration has exceeded a predetermined second threshold acceleration (for example a second threshold acceleration G2) greater than the first threshold acceleration (for example step S07), and in the case where the acceleration has exceeded the second threshold acceleration, cutting off the power supply line (for example S08).
As a result, the fuel supply cutoff operation and the power supply cutoff operation can be appropriately controlled in accordance with the magnitude of the shock at the time of a vehicle collision. Hence the inter-electrode pressure of the fuel cell can be precisely controlled corresponding to collision conditions, so that the solid polymer electrolyte membrane can be even more reliably protected.